Method and device for fragmenting multimedia data

ABSTRACT

The invention relates to a method of fragmenting multimedia data (D′ 5,  D′ 6,  D′ 7,  . . . D′ 11, ) associated with navigation nodes (N′ 5 , N′ 6 , N′ 7 , . . . , N′ 11 ), a node (N′ i ) controlling access to an associated data item (D′ i ) and to a next node (N′ i+1 ).  
     In accordance with the invention, the invention is characterized in that,  
     nodes (N′ 6 , N′ 7 , N′ 8 , and N′ 9 ) and data (D′ 6,  D′ 7,  D′ 8 , and D′ 9 ) associated with the latter in a successive manner are grouped into a temporary cell (C′ t ), comprising a starting node (N′ 5 ) and the data (D′ 5 ) associated with this node, each node grouped into the temporary cell following a node already included in this temporary cell until the size of the temporary cell reaches a threshold value, then  
     a pair of nodes (N′ 7 ; N′ 8 ) which follow one another, of the temporary cell (C′ t ), minimizing a parameter (T i ) dependent on the number of data common to the data (D′ 7 ; D′ 8 ) associated with the two nodes (N′ 7 ; N′ 8 ) of the pair is identified, a definitive cell (C′ 5 , C′ 6 , C′ 7 ) being formed with the data (D′ 5 , D′ 6 , D′ 7 ) grouped into the temporary cell prior to the data (D′ 7 ) associated with the first node (N′ 7 ) of the pair.

[0001] The present invention pertains to a method and to a device forfragmenting multimedia data, in particular data associated withnavigation nodes.

BACKGROUND OF THE INVENTION

[0002] The throughput of data transmitted via telecommunicationnetworks, such as the Internet network, and the diversity of these dataare constantly increasing, a growing number of terminals and of serversusing these networks to transmit or receive data of diverse natures, forexample, relating to audio and/or video documents, to programs, totexts, to graphical data coding two- or three-dimensional images, orelse to texts with hyperlinks allowing access to new data.

[0003] When documents comprise data of various natures, these documentsand these data are referred to hereinbelow as multimedia.

[0004] The operations performed with data D₀, D₁, D₂, D₃ and D₄ (FIG. 1)such as their coding/decoding, their transmission, their receptionand/or their display are simpler and faster to carry out when these dataare grouped or fragmented into cells C₀, C₁, C_(2/3) and C₄.

[0005] Such a fragmentation makes it possible, for example, to performthe multiplexing of these data during their transmission, or to carryout their processing in tandem with their reception.

[0006] Stated otherwise, a fragmentation of the data into cellsoptimizes the use of the limited, in terms of memory capacity andcomputational capacity, of the various terminals and servers processingthese data, as well as the use of the limited, for example in terms ofbandwidth, transmission resources of the networks.

[0007] Moreover, it is known to associate navigation nodes N₀, N₁, N₂,N₃ and N₄ with data D₀, D₁, D₂, D₃ and D₄ so as to determine the orderof access to the latter. For this purpose, each node N_(i) comprisesmeans for identifying data D_(i) which are associated therewith, as wellas means for identifying at least one next node N_((i+1)). Statedotherwise, access to a node N_((i+1)) and to the data D_((i+1))associated therewith is carried out commencing with a previous nodeN_(i).

[0008] As represented in FIG. 1, each cell C_(i) can include the node(s)N_(i) associated with the data D_(i) included in this cell C_(i).

[0009] A navigation graph can be composed of successive nodes such thata node N_(i) is connected to a single previous node N_(i−1) and to asingle next node N_(i+1). In this case, such a graph is said to belinear or one-dimensional.

[0010] Conversely, a graph can comprise nodes, such as the nodes N₁ orN₄, connected to several nodes. The navigation graph is then said to benonlinear or multidimensional. In this case, two nodes N₂ and N₄ may benext nodes of one and the same node N₁ (respectively two nodes N₁ and N₃may be previous nodes of one and the same node N₄). Moreover, the nodeN₁ being the next to node N₀, the nodes N₂, N₄ and N₀ are referred tohereinbelow as neighbouring nodes of N₀.

[0011] When distinct cells C_(i) and C_(k) comprise identical orredundant data D_(i) and D_(k), these cells C_(i) and C_(k) are said tobe redundant. Redundant data such as these are frequently used inmultimedia documents where identical data are used for variousapplications. For example, in an electronic book, one and the same imagemay be used for the display of various different pages, in which casethe data relating to the image are present in each of the cells relatingto these pages.

[0012] In another example relating to graphical data, data coding anobject may be present in cells specific to distinct viewpoints of ascene comprising this object.

[0013] However, it is advisable to limit the generation of redundantcells during the fragmentation of data so as to allow faster and simplerprocessing of the data since the processing of redundant cells causesthe repeated processing of identical data. For example, the transmittingof redundant cells requires the repeated transmitting of redundant data.

[0014] Stated otherwise, to optimize the fragmentation of multimediadata, it is advisable to group the identical or redundant data into oneand the same cell.

[0015] To fragment a set of data into cells, it is known to form datacells by considering the quantity of data included in a cell asfragmentation parameter. Stated otherwise, a data cell is generated bygrouping neighbouring data into a cell until the latter reaches a givensize. Such a method has the drawback of not optimizing the fragmentationof the data in such a way as to avoid the formation of redundant cells.

[0016] It is also known to use navigation nodes associated with thesedata and to consider the nature and/or the application of these data.For this purpose, each node N_(i) comprises means determining the natureand/or the application of the data associated therewith in such a way asto allow their fragmentation by grouping the data relating to one andthe same nature or to one and the same application. Thus, when adocument comprises several pages of text, the text data D_(i) relatingto these pages may be fragmented in such a way that the data D_(i) of acell C_(k) are specific to a page k of the document.

[0017] Thereupon, the transmission of a cell C_(k) will comprise thedata D_(k) relating to the page k of the document. In this case, forexample, the reception of the first data cells C₁, C₂ . . . and C_(k)allows a user to process pages 1, 2, . . . k while the succeeding pagesare being transmitted.

[0018] According to another example, data coding images in threedimensions are generally fragmented as a function of the viewpointsrelating to a scene and/or to an object. For example, a cell C_(k) mayconstitute a representation of a scene according to a first viewpoint,while a next cell C_(k+1), that is to say one which is accessible fromthe cell C_(k), may comprise data relating to a second viewpoint closeto the first so that the switch from the first cell C_(k) to the secondcell C_(k+1) corresponds to a displacement of the viewpoint.

[0019] According to another example, when the data code a residencecomprising several rooms, the data D_(i) of a cell C_(k) may relate to aroom of this residence, while the data D_(n) of a next cell C_(k+1) mayrelate to a neighbouring room. In this case, the switch from a cellC_(k) to a next cell C_(k+1) will be representative of the switch fromone room to a neighbouring room.

[0020] However, these fragmentation methods take into account the natureand/or the application of the fragmented data and they therefore cannotbe used to fragment multimedia data, of various natures, for whichdiverse applications, such as graphics and audio, are requiredsimultaneously.

[0021] To perform the fragmentation of data relating to images in threedimensions, known fragmentation algorithms use representation criteriasuch that each node comprises indications relating to a viewpoint of ascene and/or of an object which are coded by the data associatedtherewith. For example, known object search algorithms described byTELLER and SEQUIN in the article entitled “Visibility preprocessing forinteractive walkthroughs” published in the journal SIGG-GRAPH, 91 whichmay be implemented to identify an object, coded in an image, andallocate a specific cell to the data relating to this object.

[0022] However, the method described in this document is peculiar toarchitectural environments, such as that of a building, the cells C_(k)being predefined so as to comprise graphic images of like nature whichrelate to an image limited by vertical partitions such as walls. It doesnot therefore make it possible to fragment graphical data relating to asector other than architecture. In a manner similar to the methodsdescribed above, it does not therefore make it possible to fragmentmultimedia data.

[0023] Patent DE19723102 from MEDIA DESIGN GES MULTIMEDIA & ONLINE PUBpublished on Nov. 12, 1998 entitled “Verfahren zum Darstellen von undnavigieren in umfangreichen, Grafikelemente enthaltenden Dateien”discloses a method of fragmenting data which allocates cartographic datarelating to a two-dimensional geographical location map to each cellC_(k). This method of fragmentation has, in a manner similar to themethods described above, the drawback of depending on the nature of thefragmented data, namely of the two-dimensional cartographic data.Moreover, this method does not handle the case of redundant data whichit is advisable to group into one and the same cell as described above.

[0024] Similarly, International Patent Application No. WO 0016307 ofMICROSOFT entitled “Method and apparatus for visualising and exploringlarge hierarchical structures” discloses a method making it possible toallocate a navigation graph to data with a view to their fragmentation.However, such fragmentation can be applied only to data between which aprior hierarchy is established. Moreover, it does not make it possibleto optimize the fragmentation of data as a function of their redundancy.

[0025] In a last example, U.S. Pat. No. 6,014,671 (IBM) published onJan. 11, 2000 entitled “Interactive retrieval and catching ofmultidimensional data using view elements” discloses a method making itpossible to fragment a picture, in particular one taken from asatellite, and to generate a navigation graph according to spatial ortemporal criteria. In a manner similar to the patent described above,this patent describes a fragmentation method relating to data of likenatures which does not consider the case of redundant multimedia data.

BRIEF SUMMARY OF THE INVENTION

[0026] The present invention remedies these drawbacks by making itpossible to fragment multimedia data, that is to say redundant data ofdiverse natures, independently of their function and/or of their natureby means of their navigation graph.

[0027] More precisely, the invention relates to a method of fragmentingmultimedia data associated with navigation nodes, a node controllingaccess to an associated data item and to at least one next node,

[0028] characterized in that,

[0029] nodes and data associated with the latter in a successive mannerare grouped into a temporary cell, comprising a starting node and thedata associated with this node, each node grouped into the temporarycell following a node already included in this temporary cell until thesize of the temporary cell reaches a threshold value, then

[0030] a pair of nodes which follow one another, of the temporary cell,minimizing a parameter dependent on the number of data common to thedata associated with the two nodes of the pair is identified, adefinitive cell being formed with the data grouped into the temporarycell prior to the data associated with the first node of the pair.

[0031] By virtue of such a method, multimedia data may be fragmentedindependently of their nature and of their application, thisfragmentation being based on the use of the navigation nodes associatedwith the data.

[0032] Moreover, as a function of a criterion limiting the size of thetemporary cell, it may be possible to determine a threshold in such away as to generate cells whose size is adapted to a use such as themultiplexed transmission of data.

[0033] Furthermore, the use of a fragmentation parameter proportional tothe number of data common to the data associated with the two nodes ofthe pair tends to form substantially independent cells, that is to sayones which can be processed separately, for example in tandem with theirreception by a terminal.

[0034] Finally, the method in accordance with the invention generatescells which are optimized in relation to redundant data since redundantdata will generally be included in one and the same cell, thusfacilitating their processing as described above. Stated otherwise, thenumber of redundant cells generated by the method in accordance with theinvention is generally less than the number of redundant cells generatedby a known method of fragmentation.

[0035] In one embodiment, the parameter minimized by a pair of nodes inproportion to the number of data common to the data associated with thetwo nodes of the identified pair is determined.

[0036] In one embodiment, the threshold size of the temporary cell isdetermined as a function of the quantity of data grouped into this cellor as a function of the number of nodes grouped into this cell.

[0037] In one embodiment, use is made of the second node of the pairidentified as starting node or another as yet ungrouped node to performa fragmentation of data following this second node by repeating theoperations performed during the first fragmentation.

[0038] In one embodiment, the parameter is determined in a mannerinversely proportional to the quantity of data associated with one ofthe nodes of the identified pair.

[0039] In one embodiment, the parameter is determined in proportion tothe ratio between the number of nodes grouped into the temporary cellprior to the first node of the identified pair of nodes and the numberof nodes in the temporary cell.

[0040] In one embodiment, the multimedia data comprise data relating toat least one of the following documents: an audio document, a videodocument, a program, a text document.

[0041] In this case, according to one embodiment, the video datacorrespond to at least one of the following elements: an image, asequence of images, this or these images being two- orthree-dimensional, a panorama, graphical data.

[0042] According to one embodiment, the images relating to viewpoints ofscenes or of objects, neighbouring nodes correspond to viewpoints closeto these scenes or to these objects.

[0043] The invention also relates to a method of fragmenting multimediadata which are not associated with a navigation graph. Such a method ischaracterized in that navigation nodes are associated with these data asa function of their nature and/or their function, a compression of thesedata is performed by eliminating the redundant data, the data retainedbeing associated with the node relating to the data eliminated, andthese data are fragmented according to a method of fragmentation inaccordance with one of the embodiments of the fragmentation methoddescribed above.

[0044] In one embodiment, the data considered comprising video datarelating to real images and to synthetic images, the navigation nodesare associated with the multimedia data by imposing access to the datarelating to real images.

[0045] The invention also relates to a computer program productcomprising program code instructions for executing the steps of themethod of fragmenting multimedia data according to one of theembodiments of a fragmentation method as defined above, when the programis executed on a computer.

[0046] The invention also pertains to a device for fragmentingmultimedia data associated with navigation nodes comprising:

[0047] means for accessing a data item by means of a node associatedwith this data item,

[0048] means for determining access to a second node, the so-called nextnode, from a first node, the so-called previous node,

[0049] characterized in that it comprises:

[0050] means for grouping, commencing with a predetermined startingnode, into a temporary cell, data whose associated nodes follow oneanother until this cell reaches a threshold size,

[0051] means for identifying a pair of next nodes minimizing a parameterproportional to the number of data common to the data associated withthe two nodes of the pair and

[0052] means for forming a cell with the data associated with the firstnode of the pair and with the nodes previous to the latter node,

[0053] the said device preferably being adapted to implement a methodaccording to the invention.

[0054] In one embodiment, the device comprises means for determining theparameter in proportion to the number of data common to the dataassociated with the two nodes of the identified pair.

[0055] According to one embodiment, the device comprises means fordetermining the threshold size of the temporary cell as a function ofthe quantity of data grouped into this cell or as a function of thenumber of nodes grouped into this cell.

[0056] According to one embodiment, the device comprises means for usingthe second node of the pair identified as starting node for performing afragmentation of data following this second node by repeating theoperations performed during the first fragmentation.

[0057] In one embodiment, the device comprises means for determining theparameter in a manner inversely proportional to the quantity of dataassociated with one of the nodes of the identified pair.

[0058] According to one embodiment, the device comprises means fordetermining the parameter in proportion to the ratio between the numberof nodes grouped into the temporary cell prior to the first node of theidentified pair of nodes and the number of nodes in the temporary cell.

[0059] In one embodiment, the device comprises means for processingmultimedia data relating to at least one of the following documents: anaudio document, a video document, a program.

[0060] In this case, according to one embodiment, the device comprisesmeans for processing video data corresponding to at least one of thefollowing elements: an image, a sequence of images, this or these imagesbeing two- or three-dimensional.

[0061] According to one embodiment, the images relating to viewpoints ofscenes or of objects, the device comprises means for processing nodessuch that neighbouring nodes correspond to viewpoints close to thesescenes or to these objects.

[0062] In one embodiment, the device for fragmenting multimedia datacomprises means for associating navigation nodes with these data as afunction of their nature and/or their function, for performing acompression of these data by eliminating the redundant data, the dataretained being associated with the node relating to the data eliminated,and for fragmenting these data according to a method of fragmentation inaccordance with one of the embodiments described above.

[0063] In this case, according to one embodiment, the data consideredcomprising video data relating to real images and to synthetic images,the device comprises means for associating the navigation nodes with themultimedia data so as to impose access to the data relating to realimages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Other characteristics and advantages of the invention will becomeapparent with the description, given hereinbelow without limitation, ofcertain of its modes of embodiment, while referring to the appendeddrawings, in which:

[0065]FIG. 1, already described, represents cells comprising nodesassociated with multimedia data in a known manner, and

[0066]FIG. 2 represents cells comprising nodes associated withmultimedia data fragmented in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0067] It is recalled that the invention makes it possible to fragmentmultimedia data D₅′, D₆′, D₇′ D₈′, D₉′, D′₁₀ and D′₁₁ (FIG. 2)associated with a navigation graph comprising nodes N₅′, N₆′, N₇′ N₈′,N₉′, N′₁₀ and N′₁₁, each node N_(i)′ determining access to the dataD_(i)′ associated therewith as described above.

[0068] However, it is possible that the multimedia data D_(i)′ to befragmented are not associated, initially, with a navigation graph. Inthis case, it is necessary to generate this graph before fragmenting themultimedia data.

[0069] Such generation can be performed, for example, as a function ofthe document comprising the data D_(i)′. Thus, considering a multimediadocument formed of pages comprising hypertext links and images, thenavigation graph may be generated by allocating cells to each page ofthis document while the nodes of each cell correspond to the variousdata of each page.

[0070] If the multimedia data relate to images of scenes or of objects,the navigation graph may be composed of nodes relating to the variouspossible viewpoints of one and the same scene or of one and the sameobject represented.

[0071] In this case, it should be noted that numerous applications, suchas video games, use multimedia data relating to real images in order torepresent scenes. Therefore, it may be advantageous to generate thenavigation graph in such a way as to limit access to these real datawhose processing is simpler and faster than the processing of datarelating to synthetic images.

[0072] In another example, if the data relate to a computer-aided designtool and comprise a hierarchization of the data as a function of thevarious elements or items used for the design, the navigation graph maybe composed of nodes representative of this hierarchy.

[0073] In a general manner, if the data are organized according to apreexisting structure, such as a grid or a file structure, a navigationgraph may be obtained from this original structure.

[0074] When the multimedia data are associated with a navigation graph,a compression of these data is performed by means of this navigationgraph. To do this, redundant data D_(i)′ and D_(n)′ are identified andprocessed by eliminating data, for example D_(n)′, and by associatingthe nodes N_(i)′ and N_(n)′ with the remaining data D_(i)′, referred tohereinbelow as D_(i)′/D_(n)′. In FIG. 2, the nodes N₉′ and N₈′ are thusassociated with data D₈′/D₉′. Likewise, the nodes N₅′ and N₆′(respectively the nodes N₆′ and N₇′) are associated with data D₅′/D₆′(respectively D₆′/D₇′).

[0075] Other forms of compression are possible. Thus, in the case ofdata relating to visual representations associated with a navigationgraph, French Patent No. 9911671 entitled “Procédé de construction d'unmodéle de scéne 3D par analyse de séquence d'images” [Method ofconstructing a 3D scene model by analysing image sequences] dated Sep.17, 1999 filed in the name of Thomson Multimedia, discloses a method forperforming a compression of data relating to images in three dimensionsand associated with a navigation graph.

[0076] For video databases containing descriptions based onthree-dimensional images and with which a navigation graph isassociated, the Patent FR9911671 already cited describes procedures foradding information relating to visibility to a navigation node so as todetermine what information is necessary for the reconstruction of aviewpoint and needs to be associated with this node.

[0077] After this compression step, the multimedia data D₅′, D₆′, D₇′D₈′, D₉′, D′₁₀ and D′₁₁ are fragmented into various data cells C′_(i).In accordance with the invention, this fragmentation is performed byperforming the following operations:

[0078] Firstly, a starting node N₅′ is determined such that from thisnode N₅′ the entire set of data D′₅, D′₆, D′₇, D′₈, D′_(g), D′₁₀ andD′₁₁ to be fragmented is accessed, via this starting node, and nodesN′₆, N′₇, N′₈, N′₉, N′₁₀ and N′₁₁ following the latter are accessed.

[0079] It should be stressed that, as represented in FIG. 2, the methodof fragmentation in accordance with the invention is applied to dataassociated with a nonlinear navigation graph, the node N′₅ beingassociated with two nodes N′₆ and N′₇.

[0080] Thereafter, data D′₅, D′₆, D′₇, D′₈, D′₉ selected successivelyare grouped into a temporary cell C_(t) by considering, commencing withthe starting node N′₅, the data associated with a node neighbouring thestarting node N′₅ or a node whose associated data have been grouped intothe temporary cell. For example, the data D′₆ whose node N′₆ neighboursthe node N′₅ are grouped into the temporary cell C_(t). Thereafter, thedata D′₇ whose node N′₇ also neighbours the node N′₅ are grouped.

[0081] Likewise, the data D′₈ and D′₉ are grouped successively into thetemporary cell C_(t) by considering the nodes N′₈ and N′₉ associatedwith them to be neighbours of a node included in the temporary cellC_(t). In this example, the nodes associated with the data are alsogrouped into the temporary cell.

[0082] Such a grouping is performed until the number D′₅, D′₆, D′₇, D′₈,D′₉ of data included in the temporary cell reaches a threshold value. Ina variant, a limit size of the temporary cell is determined as afunction of the number of nodes included in this temporary cell.

[0083] When the temporary cell has reached the threshold size, a pair ofsuccessive nodes (N′₇; N′₈), that is to say of which a first node N′₇precedes a second, next, node N′₈, which minimizes a parameter T_(i)proportional to the number of data D_(c)′ common to the data (D′₇; D′₈)associated with the two nodes (N′₇; N′₈) of the identified pair, isidentified. In this example, this parameter T_(i) takes the followingform:

T=((T−(i−5))/T)*r _(i)

[0084] Where T is the total number of nodes included in the temporarycell C′_(t), i−5 is the number of node(s) grouped into the temporarycell prior to the first node N₇′ of the relevant pair of nodes and r_(i)is equal to the ratio between D_(c)′, the number of data common to D′₇and D′₈, and D′_(max), the number of data associated with one of thenodes N′₇ and N′₈ of the pair.

[0085] Finally, a definitive cell C′_(5/6/7) is formed comprising thedata (D′₅, D′₆, D′₇) grouped successively into the temporary cell untilthe data associated with the first node N′₇ of the pair.

[0086] Subsequently, new definitive cells are formed by repeating theoperations described above for which the second node (N′₈) of theidentified pair is used as starting node.

[0087] In a variant of the invention, a node other than this node (N′₈)of the identified pair is used as starting node.

[0088] It is apparent that the method in accordance with the inventiontends to limit the formation of redundant cells, since the limit of thedefinitive cells is obtained with the aid of a pair of nodes (N′₇; N′₈)which minimizes a parameter T_(i) proportional to the number of datacommon to two neighbouring nodes, that is to say a pair for which thereis no or hardly any redundancy of data between cells.

[0089] Stated otherwise, the method in accordance with the inventiontends to group the redundant data into definitive cells C′_(5/6/7),thereby facilitating their processing as described above.

[0090] Subsequently, the fragmentation of the data associated with thesecond node N₈ of the pair (N₇′; N₈′) identified and with the nodes(N₉′, N₁₀′, . . . N_(z)′) following the latter node is performed byrepeating the operations described above while taking the second node(N′₈) of the identified pair as starting node in order to form a newtemporary cell.

[0091] As described above, in a variant of the invention, a node otherthan the second node of the identified pair is used as starting node fora new fragmentation.

1. Method of fragmenting multimedia data associated with navigationnodes, a node controlling access to an associated data item and to atleast one next node, wherein, nodes and data associated with the latterin a successive manner are grouped into a temporary cell, comprising astarting node and the data associated with this node, each node groupedinto the temporary cell following a node already included in thistemporary cell until the size of the temporary cell reaches a thresholdvalue, then a pair of nodes which follow one another, of the temporarycell, minimizing a parameter dependent on the number of data common tothe data associated with the two nodes of the pair is identified, adefinitive cell being formed with the data grouped into the temporarycell prior to the data associated with the first node of the pair. 2.Method according to claim 1, wherein the parameter minimized by a pairof nodes in proportion to the number of data common to the dataassociated with the two nodes of the identified pair is determined. 3.Method according to claim 1, wherein the threshold size of the temporarycell is determined as a function of the quantity of data grouped intothis cell or as a function of the number of nodes grouped into thiscell.
 4. Method according to claim 1, wherein use is made of the secondnode of the pair identified as starting node or another as yet ungroupednode to perform a fragmentation of data following this second node byrepeating the operations performed during the first fragmentation. 5.Method according to claim 1 wherein the parameter is determined in amanner inversely proportional to the quantity of data associated withone of the nodes of the identified pair.
 6. Method according to claim 1,wherein the parameter is determined in proportion to the ratio betweenthe number of nodes grouped into the temporary cell prior to the firstnode of the identified pair of nodes and the number of nodes in thetemporary cell.
 7. Method according to claim 1, wherein the multimediadata comprise data relating to at least one of the following documents:an audio document, a video document, a program, a text document. 8.Method according to claim 6, wherein the video data correspond to atleast one of the following elements: an image, a sequence of images,this or these images being two- or three-dimensional, a panorama,graphical data.
 9. Method according to claim 8, wherein the imagesrelating to viewpoints of scenes or of objects, neighbouring nodescorrespond to viewpoints close to these scenes or to these objects. 10.Method of fragmenting multimedia data, wherein navigation nodes areassociated with these data as a function of their nature and/or theirfunction, a compression of these data is performed by eliminating theredundant data, the data retained being associated with the noderelating to the data eliminated, and these data are fragmented accordingto a method of fragmentation in accordance with one of the precedingclaims.
 11. Method according to claim 9, wherein the data consideredcomprising video data relating to real images and to synthetic images,the navigation nodes are associated with the multimedia data by imposingaccess to the data relating to real images.
 12. Computer program productcomprising program code instructions for executing the steps of themethod of fragmenting multimedia data according to claim 1, when theprogram is executed on a computer.
 13. Device for fragmenting multimediadata associated with navigation nodes comprising: means for accessing adata item by means of a node associated with this data item, means fordetermining access to a second node, the so-called next node, from afirst node, the so-called previous node, wherein it comprises: means forgrouping, commencing with a predetermined starting node, into atemporary cell, data whose associated nodes follow one another untilthis cell reaches a threshold size, means for identifying a pair of nextnodes minimizing a parameter proportional to the number of data commonto the data associated with the two nodes of the pair and means forforming a cell with the data associated with the first node of the pairand with the nodes previous to the latter node, the said devicepreferably being adapted to implement a method according to claim 1.